1. Field of the Invention
The present invention relates to a plastic molding process using an injection molding machine or extruder. In particular, the present invention is directed to a low pressure injection molding machine and a process for forming a shaped article by injecting a foamed thermoplastic polymeric resin formed in the machine into a mold at a relatively low pressure according to the present invention using the present injection molding machine. The foamed characteristic retards shrinkage of the shaped article as the thermoplastic material cools, and the process can be carried out using waste or used thermoplastic material.
2. Prior Art
In conventional high pressure injection molding machines, a molten thermoplastic material is injected into a mold at a very high pressure, i.e., upwards of several thousand pounds per square inch. This pressure is maintained on the mold as the plastic cools and the high pressure retards shrinkage of the thermoplastic material to an appreciable amount. The problem is that high pressure molds are very expensive.